A monster modifier is one of the additional special attributes a monster can have, such as being extra strong or fast. Monsters change between the difficulties, and bosses spawn with all sorts of interesting properties.

Minions are the monsters that spawn around a boss. They share some properties with the boss (such as Extra Fast and Extra Strong), and are tougher than normal monsters. They also receive considerable bonuses to their hit points, compared to standard monsters of their type.

Normal = 3x hit points.

Nightmare = 1.75x hit points.

Hell = 1.5x hit points.

Champions receive hit point bonuses over standard monsters of their type.

A variety of different types of Champions were added in D2X. They receive various bonuses to make them tougher than standard monsters of their type. Most champion monsters spawn in bright colors, making them stand out from standard monsters. Ghostly champions are translucent, and are the only type of Hell Bovine that look any different from all the rest.

Note: This modifier will set the physical resistance to 80% not increase it by 80%. You may found a "Immune to Physical" ghostly monster but it in fact only has 80% resistance and the description is wrong.

Boss Properties are semi-randomly generated. Random bosses spawn with 1 random property on normal, 2 on Nightmare, and 3 on Hell. Superuniques generally have one or more fixed properties at all times, and many of them gain 1 additional on Nightmare and 2 on Hell. Act Bosses and Uber monsters do not get random properties; all their properties are preset, and they all grow more difficult on higher difficulties.

Explodes upon death, dealing 75%-100% of max hit points over a 4 yard radius. (This death explosion was nerfed in v1.09. Prior to that version, a number of very high hit point Superuniques on Hell difficulty could instantly kill any Characters in range.

When attacked from melee range, bosses with this property will sometimes teleport to a random location when their hit points drop below 33%. The monster will partially heal when it teleports.

This property was very difficult to deal with in early versions of Diablo II, since it let monsters regain their full hit points each time they teleported. Battles between low damage characters and high hit point teleporting monsters could go on almost indefinitely. This property was nerfed in subsequent patches and in v1.09+ monsters teleport much less often, and heal only slightly when they do.

Some monsters, such as Baal and Uber Izual, will teleport without regaining hit points.

This property was removed from the game in v1.04. Before then it was most often noted as one of Lord de Seis' modifiers, as you can see in old screenshots. The thief property created a chance for potions to drop from the player's belt whenever the thief boss hit them with a melee or ranged attack. It was an interesting effect, but buggy, and could cause the game to crash under some circumstances. For instance, when a Barbarian is in mid-Whirlwind, his belt gets red'ed out, and he can not access his belt.